If you want to import OLM data to Outlook PST format without any hassle then try vMail OLM to PST Converter tool. This professional application supports all Windows OS and allows exporting data from OLM to PST, Office 365, EML, MSG, etc. Users can also use the software on the bulk mailbox and migrate all of them at once. The free version of the tool converts 30 items from each folder.
Manual technique: OLM to PST conversion
Open Gmail or any other webmail then, click on Settings.
InSettings, select Forwarding and POP/IMAP tab.
Now check the status of IMAP; if it is not enabled, then enable IMAP and Save changes.